What Diff fluid does everyone run?

CruzinQueen

Original poster
Member
Dec 30, 2011
46
Okay - I'm planning to change my fluids very soon since the lift has been installed and the truck has 76K on him. I understand that the only T-Case fluid to run is the GM stuff, but I've been researching the gear oils and not found a difinitive answer. I'm torn between Lucas, Royal Purple, and Mobil I. I do not plan on having to change this for another 5 years or so, therefore money is not a concern. I want the absolute best for my vehicle. What do you all recommend?
 

fishguy1123

Member
Dec 5, 2011
310
I just switched out to Mobile 1. Not sure if it's the "best" but I think I'll be happy with it. If you don't have a suction pump for gear oil, get one! Only 11 or 12 bucks and makes the job soooo much easier and faster.
 

STLtrailbSS

Member
Dec 4, 2011
1,617
In the SS I will be running Royal Purple 75w-90. I put a lot of strain on my diff and royal has the friction additive which is recomended for many differentials. I have found that if not running royal purple a lot of guys will buy the acdelco modifier to run in there diffs outside of GM cars.
 

jbones

Member
Dec 5, 2011
658
I put Mobil 1 Syn LS 75wx90 in the front and Valoline full Syn LS 75wx90 in the rear.

And yes, you are correct, us the the GM Performance Auto Trak II Transfer Case Fluid only.

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davenay67

Member
Jan 16, 2012
217
STLtrailbSS said:
I put a lot of strain on my diff and royal has the friction additive which is recomended for many differentials.

Most, if not all, synthetics have the friction additive required for diffs. Even if you run a non-synthetic diff oil you still need to add the additive if you want your diff to last.


I run Mobil 1 75W90 in the TB and Royal Purple 75W140 (if was a steal of a deal, will use Mobil 1 next time) in my Jeep TJ. Some of the gurus on the Jeep forum recommend the non-synth plus the limited slip gear oil additive in preference to synth, something about the synth expanding more with heat..??
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
davenay67 said:
...Some of the gurus on the Jeep forum recommend the non-synth plus the limited slip gear oil additive in preference to synth, something about the synth expanding more with heat..??
I don't see any reason to take a Jeep forum member's recommendation over our own Owner's and Shop Manuals recommendation for full synthetic 75W90. I use Mobil 1 75W90LS because it's the same price here as the non-LS additive stuff if the store even offers a choice, and the clutch packs in the G80 locker have been reported to run quieter in some cases with the LS additive. Although the G80 is not a true LS diff, the clutch packs used to activate the locking pawls can benefit from the additive. Although the 2004 shop manual makes no mention of needing it.
 

davenay67

Member
Jan 16, 2012
217
the roadie said:
I don't see any reason to take a Jeep forum member's recommendation over our own Owner's and Shop Manuals recommendation for full synthetic 75W90.

I wasn't implying that you should, it was merely informational to show that the LS additive is the important ingredient in the fluid. If you note, I personally run full synthetic in both of my vehicles diffs.

FWIW....the Jeep rear diff scares me a lot more than the TB rear diff, but the IS junk at the front of the TB scares me even more than the front diff in the Jeep.
 

navigator

Member
Dec 3, 2011
504
my 06 manual only lists the additive for the SS.
I just run Royal Purple.
MY auto store only had one bottle of the Mobile-1 so they gave me the RP for the same price.
 

STLtrailbSS

Member
Dec 4, 2011
1,617
navigator said:
my 06 manual only lists the additive for the SS.
I just run Royal Purple.
MY auto store only had one bottle of the Mobile-1 so they gave me the RP for the same price.

thats a steal!!!! lol very nice
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
jham said:
I am running royal purple in my diff on a side note when it gets below 10 here my locker stays locked till the fluid gets warmed up

Does that just start happening when you changed to RP?
That doesn't seem to be a great endorsement for RP. :twocents:
 

Voymom

Member
Feb 3, 2012
2,523
If your not planning on repeating this procedure again for another 5yrs, I would suggest just going with the GM stuff. It's expensive yes, but like you said money should not be an issue since it isn't a regular thing that needs done. I plan on using the GM stuff when I do mine this spring. :twocents:
 

barron03

Member
Nov 20, 2011
960
I use Mobil 1 LS 75w-140 in the front and rear diff .
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Voymom said:
If your not planning on repeating this procedure again for another 5yrs, I would suggest just going with the GM stuff. It's expensive yes, but like you said money should not be an issue since it isn't a regular thing that needs done. I plan on using the GM stuff when I do mine this spring. :twocents:
That's essentially rewarding GM for their rip-off parts counter list prices. $35/bottle LIST?!? :eek: And here I thought you were an enthusiast. :rolleyes:

It's not always about the price - it's about the principle. :yes:

:raspberry:
 

Juicy K

Member
Feb 14, 2012
433
Indianapolis, Indiana
I am running Royal Purple Front and Rear, the old fluids were really dirty, who knows if they were ever changed the first 102,000 miles of its life, but It may be my mind but it seemed to drive a little smoother after replacing the fluids. And BTW I know what a difference changing very old dirty Auto Trac II can make. It was amazing after I switched that one out. :biggrin:
 

Voymom

Member
Feb 3, 2012
2,523
the roadie said:
That's essentially rewarding GM for their rip-off parts counter list prices. $35/bottle LIST?!? :eek: And here I thought you were an enthusiast. :rolleyes:

It's not always about the price - it's about the principle. :yes:

:raspberry:

Yes, but so is buying their trucks :wink:
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
I run Mobile One, but need to figure ouot what to run with the new LockRight going in. I was told to avoid the LS additive stuff, but cant find real info to back that up.
 

GregT

Member
Jan 12, 2012
58
Mobile 1 here :thumbsup:
 

Iahawkeye

Member
Jan 24, 2012
52
GregT said:
Mobile 1 here :thumbsup:

That is what I use too.

I have been looking for the last 1/2 hour to try and find a maintinance schedule for the differentials. How often should you change them? I changed them at 75,000 the first time but I can't seem to find the schedule anywhere.

Thanks.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
Iahawkeye said:
That is what I use too.

I have been looking for the last 1/2 hour to try and find a maintinance schedule for the differentials. How often should you change them? I changed them at 75,000 the first time but I can't seem to find the schedule anywhere.

Thanks.


I've never found a schedule for the diffs either.
The only thing the manual calls for is checking the level and topping up as needed.
A lot of the off roaders and the guys that do a lot of towing, change at 50k.
 

Tofer76

Member
Dec 8, 2011
148
MAY03LT said:
That's what I use.:yes:

as do i

Wooluf1952 said:
I've never found a schedule for the diffs either.
The only thing the manual calls for is checking the level and topping up as needed.
A lot of the off roaders and the guys that do a lot of towing, change at 50k.

i will just do the front, rear, and trans case every 2 years . hell it dont cost that much over all
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
I do it every 50K or whenever I change axles, whichever comes first. :rotfl:

Normal street drivers can justify 100K IMHO. It is very unusual that GM doesn't publish a mileage interval, yet some dealers nag their victim/owners to get it done every 25-50K. Greedy criminals. :mad:
 

Iahawkeye

Member
Jan 24, 2012
52
the roadie said:
I do it every 50K or whenever I change axles, whichever comes first. :rotfl:

Normal street drivers can justify 100K IMHO. It is very unusual that GM doesn't publish a mileage interval, yet some dealers nag their victim/owners to get it done every 25-50K. Greedy criminals. :mad:

So it appears that 75,000 miles may be a happy medium for a family hauler. Thanks for your input.
 

Taz6056

Member
Dec 21, 2011
49
+1 For Royal Purple. Quieted a chattered in the rear diff I didn't even know I had. Haha, so well in fact, my girlfriend, after helping me change the transfer case and both diff fluids gushed about how nice the ride, and wanted us to change the transfer case and diff fluids in her Hyundai elantra hahahahahahahaha.
 

HARDTRAILZ

Moderator
Nov 18, 2011
49,665
Just put Lucas synthetic in front diff
 

seanpooh

Member
Jan 24, 2012
461
Royal Purple for me. It's in both the front and rear differentials. I change the front more often than the back since the front fluid turns darker faster than usual. The rear stays full and purple. No set mileage on change though. I do check regularly. Transfer case is 50,000 with the Autotrak blue stuff. I also have RP in both my tranny (not purple) and engine. A very good fluid overall.
 

Mooseman

Moderator
Dec 4, 2011
25,307
Ottawa, ON
Probably not since we stay with what's recommended, 75w90. I would imagine higher viscosity would lower MPG's but shouldn't be that much.
 

Daniel644

Member
Feb 27, 2015
574
Mobil 1 full synthetic in the weight the manual calls for, did it last year sometime, and plan to do it ever 50k like it calls for, but it's just a daily driver for me, barely use the 4wd unless I get stuck in the driveway at the house I'm moving out of or hit some snow.
 

Sparky

Member
Dec 4, 2011
12,927
What would be the point of going to a thicker gear oil than what is called for?
 

dkvasnicka

Member
Jul 24, 2015
366
Czech republic, Europe
What would be the point of going to a thicker gear oil than what is called for?
I've heard some people do it for added protection on trucks that tow/haul a lot. I plan to do it to hopefully silence my rear diff, which developed a slight howl in specific scenarios and under moderate acceleration. It all started after I changed the oil in it after purchase (and probably 90k miles without change)... I must confess that I probably contributed to it myself because I was an idiot and didn't check for potential difference in capacity for the G86 and I just went by the instructions available for those with open diffs (I didn't fill it to the top, I just checked the level with a ziptie and it seemed enough, i.e. within 1 cm from the fill hole - I know it's stupid)... Long story short, I was running the diff with 0.85 qt less fluid than it needs for some time, like 2500 miles :bonk: I don't believe this is all it took and I think the diff was already on its way but I can be easily convinced otherwise :wink: I hope to know more once I open it and see the fluid and the magnet. I guess bearings are waving me goodbye or something.
 
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littleblazer

Member
Jul 6, 2014
9,265
I've heard some people do it for added protection on trucks that tow/haul a lot. I plan to do it to hopefully silence my rear diff, which developed a slight howl in specific scenarios and under moderate acceleration. It all started after I changed the oil in it after purchase (and probably 90k miles without change)... I must confess that I probably contributed to it myself because I was an idiot and didn't check for potential difference in capacity for the G86 and I just went by the instructions available for those with open diffs (I didn't fill it to the top, I just checked the level with a ziptie and it seemed enough, i.e. within 0.1 cm from the fill hole - I know it's stupid)... Long story short, I was running the diff with 0.85 qt less fluid than it needs for some time, like 2500 miles :bonk: I don't believe this is all it took and I think the diff was already on its way but I can be easily convinced otherwise :wink: I hope to know more once I open it and see the fluid and the magnet. I guess bearings are waving me goodbye or something.
Buddy of mine said GM used to not quite fill them up all the way from the factory, used to do like 3/4 full. If that is true or not I don't know. I do know the sierra spent most of its life on the factory change and it was allegedly 1 quart low. I dunno.
 

Sparky

Member
Dec 4, 2011
12,927
As far as I know full is to the bottom of the fill hole. You can't fill it more than that because, well, it runs out the fill hole :tongue:
 

triz

Member
Apr 22, 2013
746
Yeah it should pour right out the fill hole. I am using the Severe Gear fluid as well from Amsoil.
 

dkvasnicka

Member
Jul 24, 2015
366
Czech republic, Europe
Buddy of mine said GM used to not quite fill them up all the way from the factory, used to do like 3/4 full. If that is true or not I don't know. I do know the sierra spent most of its life on the factory change and it was allegedly 1 quart low. I dunno.

I'd love all that to be true because it would enable me to shift the larger portion of the blame for my problems to the fact that the diff had not been serviced properly before I bought it :wink:
 

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